1. Field of the Invention
The present invention relates to a scanning exposure apparatus and its making method, and a device manufacturing method. More particularly, the present invention relates to a scanning exposure apparatus used to manufacture semiconductor devices and liquid crystal display devices and the like in a lithographic process and the method of making the apparatus, and a device manufacturing method using the scanning exposure apparatus to manufacture microdevices such as semiconductor devices.
2. Description of the Related Art
In recent years, in the lithographic process to manufacture devices such as semiconductors, scanning exposure apparatus based on the so-called method such as a slit-and-scan method, and a step-and-scan method have been used with these exposure apparatus, a rectangular or an arcuated illumination area on the mask or a reticle where a pattern is formed (hereinafter generally referred to as a xe2x80x9creticlexe2x80x9d) is illuminated by an illumination light. The reticle and a substrate such as a wafer are synchronously moved in a one-dimensional direction, and the pattern is sequentially transferred onto the substrate.
With such an apparatus, in order to prevent the areas other than the pattern area on the reticle from being exposed during exposure, a shielding unit (also referred to as a movable reticle blind) is used (see Japanese Patent Laid-Open 04-196513 and the corresponding U.S. Pat. No. 5,473,410 for reference) to drive a movable blade restricting the illumination area on the reticle synchronously with the reticle with the conventional shielding unit, the movable blade is driven in the direction of synchronous movement by the rotational movement of a rotary motor serving as a driving source being converted into a linear motion with a feed screw or a ball screw.
In the manufacturing process of semiconductor devices, it is required to accurately overlay and transfer the pattern formed on the reticle onto the wafer.
With the conventional shielding unit, however, the rotary motor used as the driving source of the movable blade continues to rotate at a constant speed when the movable blade and the reticle are driven synchronously at a constant speed during scanning exposure. This rotation caused vibration to occur due to the rotational inertia eccentric amount, and the vibration affected other members, which in turn reduced the exposure accuracy of the scanning exposure apparatus. In addition, when the number of rotation increased, the vibration component caused by the rotation also increased. This, therefore, was a barrier to high speed of the reticle stage, in other words, a barrier to high scanning exposure performance, which led to a difficulty in improving the throughput.
To keep the vibration caused when driving the shielding unit from affecting other parts of the apparatus, a structure may be considered to physically separate the reticle blind portion including the shielding unit (movable reticle blind), the reticle stage, the wafer stage, and the main column portion (hereinafter referred to as xe2x80x9cbodyxe2x80x9d appropriately) incorporating components such as the projection optical system so that the vibration does not spread to the respective parts. The reticle blind, however, does not function as originally planned by simply decoupling the reticle blind and the main column portion.
That is, the fixed reticle blind (fixed field stop) determines the illumination area on the reticle. If, therefore, the vibration affects the fixed reticle blind independently from the body, the illumination area changes on the reticle pattern surface, and this means that the image plane illuminance loses stability during exposure. Also, for the shielding unit or the movable reticle blind to fully exercise its shielding properties, the image of the movable blade which is arranged near the surface conjugate to the reticle pattern surface has to be within the range of the shielding area of the reticle with the current scanning exposure apparatus, therefore, the vibration isolation unit (active vibration isolation unit) which isolates the main column from the vibration is required to maintain the position and posture of the main column at the initial state at all times. This is possible by controlling the vibration so that the affects of the reaction force that occurs when driving the reticle stage or wafer stage will be cancelled out almost simultaneously.
In the case, however, a damped harmonical deformation occurs to the body by the reaction force, even if the vibration isolation unit tries to control the vibration of the body to maintain the position and posture of the body at the initial state, since the body has an extremely high mass and the responsiveness of the driving portion of the vibration isolation unit (actuator) is not that high, it would be difficult to suppress the initial displacement of the body even if a counter-force was applied to cancel the vibration by monitoring the vibration, displacement, and the like.
With the scanning exposure apparatus, higher stage acceleration will be required in future, therefore, in the future scanning exposure apparatus, the tendency of creating vibration that has a vibration period faster than the response speed of the actuator is expected to increase. In such a case, as a consequence, the movable blade of the shielding unit and the reticle cannot be synchronized, therefore, the shielding properties cannot be effectively exercised.
The present invention has been made in consideration of the inconvenience of the prior art, and has as its object to provide a scanning exposure apparatus capable of reducing the influence of the vibration, caused by driving the shielding unit, on other parts of the apparatus, thereby providing a higher exposure accuracy.
According to the first aspect of the present invention, there is provided a first scanning exposure apparatus which synchronously moves a mask and a substrate to transfer a pattern on the mask onto the substrate, the exposure apparatus comprising: an illumination system which illuminates the mask with an illumination light; a driving system which drives the mask and the substrate in synchronous; a movable blade which limits an illumination area on the mask; a linear motor which drives the movable blade; and a separate portion where the linear motor is arranged, the separate portion being independent at least in respect to vibration from a main portion which exposes the substrate with an illumination light via the mask.
According to this exposure apparatus, the driving system drives the mask and substrate in synchronous in a state where the mask is illuminated by the illumination light of the illumination system. By doing so, the pattern formed on the mask is sequentially transferred onto the substrate. During this scanning exposure, in order to prevent unnecessary portions (portions on the mask other than the pattern area) from being irradiated by the illumination light, the movable blades limiting the illumination area on the mask are driven synchronously with the mask by linear motors. Therefore, problems such as vibration due to rotational inertia eccentric amount which occur when using rotary motors as in the conventional art do not occur. Also, the linear motor is arranged in a separate portion, being separate from a main portion that exposes the substrate with an illumination light via the mask and independent at least in respect to vibration. Therefore, the vibration of the linear motor is not the direct cause of vibration occurring on the main portion side. Accordingly, this removes a major factor of vibration during scanning exposure, and as a consequence, can improve the exposure precision.
With the first scanning exposure apparatus according to the present invention, the exposure apparatus can further comprise a projection optical system which is arranged in the main portion and projects the illumination light onto the substrate.
With the first scanning exposure apparatus according to the present invention, a portion of the illumination system can be arranged in the main portion, and the portion may have a fixed field stop that sets the illumination area. In such a case, the main portion that performs exposure on the substrate has a fixed field stop setting the illumination area on the pattern surface of the mask. Therefore, the fixed field stop and the main portion makes the same motion against vibration, so the illumination area of the illumination light on the substrate (the illumination area on the pattern surface of the mask) does not change. Thus, exposure on unnecessary areas (positional error generated between the illumination area and the mask) on the substrate can be avoided, and the image plane (substrate surface) illuminance stabilizes during S exposure. Also, since only the portion of the illumination system is arranged in the main portion, the total mass of the main portion side can be reduced, as well as lower the center of gravity.
In this case, the illumination system may have an optical integrator arranged in the separate portion.
With the first scanning exposure apparatus according to the present invention, the linear motors may of course be driven in a direction perpendicular to the synchronous moving direction. However, it is preferable for the linear motor to drive the movable blade in a direction corresponding to a first direction in which the mask and the substrate is synchronously moved. This is because, with linear motors, when the movable blades have entered a constantly moving state, thrust is hardly required, therefore, the linear motors are hardly the source of vibration during this state. Accordingly, in addition to improving the exposure accuracy, when a higher performance is required with the synchronous movement velocity, even if the thrust of the linear motors is increased, vibration is hardly generated during the synchronous movement. The synchronous movement velocity, therefore can be increased, which in turn leads to an improvement in throughput.
In this case, the exposure apparatus may further comprise an actuator, which drives the movable blade in a direction corresponding to a second direction and has a static holding force, the second direction being perpendicular to the first direction. In such a case, when the movable blade in respect to the second direction is static, the servo of the actuator can be cut off; therefore, hunting (vibration) is not generated.
In this case, the actuator can be arranged in the separate portion.
According to the second aspect of the present invention, there is provided a second scanning exposure apparatus which synchronously moves a mask and a substrate to transfer a pattern on the mask onto the substrate, the exposure apparatus comprising: a main portion which exposes the substrate with an illumination light via the mask; a first column where the main portion is arranged; a movable shielding member which limits an illumination area of the illumination light on the substrate in accordance with synchronous movement of the mask and the substrate; and a second column which is independent from the first column in respect to vibration, the movable shielding member being arranged in the second column.
With this exposure apparatus, the movable shielding member which is a major source of vibration during scanning exposure, is supported by the second column which is independent in respect to vibration from the first column where the main portion is arranged. Therefore, the vibration of the movable shielding member is not the direct vibration factor of the first column side. Also, the movable shielding member limits the illumination area of the illumination light on the substrate, therefore, usually only need to prevent the irradiation of illumination light for exposure on the area outside the shield strip arranged in the periphery of the pattern area on the mask. The width of the shield strip is normally 1.5-3 mm, or even wider. The accuracy required, therefore, is substantially moderate, even when considering the vibration of the main portion caused by driving the mask, the vibration of the second column caused by driving the movable shielding member, the defocus of the movable shielding member, and the distortion of the optical system. Accordingly, when the pattern formed on the mask is transferred onto the substrate with the mask moved in synchronous with the substrate based on the scanning exposure method, the movable shielding member ensures that the area outside the shield strip in the periphery of the pattern area on the mask is kept from being irradiated by the illumination light. This eliminates a major cause of vibration on the main portion side during scanning exposure, and as a consequence, the exposure accuracy can be improved.
With the second scanning exposure apparatus according to the present invention, the main portion may have a fixed field stop which sets the illumination area of the illumination light on the substrate. In such a case, since the main portion performing exposure has a fixed field stop which sets the illumination area of the illumination light on the substrate (the illumination area on the pattern surface of the mask) the fixed field stop and the main portion moves in the same way. So, the illumination area on the substrate with the illumination light (the illumination area on the pattern surface of the mask) does not change, therefore, exposure of unnecessary areas on the wafer (occurrence of a positional error between the illumination area and the mask) can be avoided, thus stabilizing the image plane (substrate surface) illuminance during exposure.
With the second scanning exposure apparatus according to the present invention, the exposure apparatus may further comprise: an illumination optical system which irradiates the illumination light onto the mask; wherein a portion of the illumination optical system is arranged in the main portion, and the fixed field stop may be arranged within the portion of the illumination optical system. In such a case, only a portion of the illumination optical system is arranged in the main portion, therefore, the total mass of the main portion can be reduced, as well as lower the center of gravity.
In this case, the fixed field stop may be arranged a predetermined distance apart from a surface conjugate with a pattern surface of the mask.
With the second scanning exposure apparatus according to the present invention, in the case a portion of the illumination optical system that includes the fixed field stop is attached to the main portion, the movable shielding member may be arranged within the illumination optical system and a portion of the illumination optical system may be located further on a side of the mask than the shielding member, the portion of the illumination optical system arranged in the main portion. In such a case, since there are almost no moving portions further on the mask side from the movable shielding portion that can be the source of vibration, factors of vibration are substantially eliminated, so the accuracy of moving the mask and the substrate in synchronous can be improved.
In this case, the movable shielding member may be arranged on a surface almost conjugate with a pattern surface of the mask.
With the second scanning exposure apparatus according to the present invention, when a portion of the illumination optical system arranged further on the mask side than the movable shielding member, is arranged in the main portion, the illumination optical system excluding the portion arranged in the main portion may be arranged in the second column. That is, the illumination optical system may be separated into the first partial optical system supported by the second column and the second partial optical system supported by the first column. In this case, the portion of the illumination optical system arranged in the first column and a remaining portion of the illumination optical system arranged in the second column may be respectively arranged in different housings. Housings, here, include frames, which house the partial illumination optical system and barrels (tightly sealed).
With the second scanning exposure apparatus according to the present invention, when a portion of the illumination optical system arranged further on the mask side than the movable shielding member, is arranged in the main portion, the main portion may have a mask stage which moves the mask in respect to the illumination light. In such a case, the motion of the mask stage against vibration can be made the same as that of the main portion, accordingly, as that of the fixed field stop against vibration arranged in the main portion.
In this case, the main portion may have a projection optical system, which projects the illumination light onto the substrate. In such a case, divergence of the optical axis of the portion of the illumination optical system arranged in the main portion and the optical axis of the projection optical system can be avoided.
With the second scanning exposure apparatus according to the present invention, in the case the exposure apparatus further comprises an illumination optical system which irradiates the illumination light onto the mask, the movable shielding member may be arranged within the illumination optical system and a portion of the illumination optical system may be located further on a side of the mask than the shielding member, the portion of the illumination optical system arranged in the main portion. In such a case, since there are almost no moving portions further on the mask side from the movable shielding portion that can be the source of vibration, factors of vibration are substantially eliminated, so the accuracy of moving the mask and the substrate in synchronous can be improved.
With the second scanning exposure apparatus according to the present invention, the exposure apparatus can further comprise an adjustment unit which adjusts a positional relationship between the movable shielding member and the main portion so as keep a positional error between the movable shielding member and the main portion within a permissible value. In such a case, when the mask and the substrate are moved in synchronous, the adjustment unit adjusts the positional relationship between the movable shielding member and the main portion so that the positional error between the movable shielding member and the main portion is kept within a permissible value. Therefore, the movable shielding member can follow-up the mask sufficiently, and does not lose its shielding properties.
In this case, when the exposure apparatus further comprises a driving unit which drives the movable shielding member during scanning exposure of the substrate with the illumination light, the adjustment unit may have a detection unit which detects information related to relative displacement between the movable shielding member and the main, portion, and may control the driving unit in accordance with the information detected by the detection unit. In such a case, the adjustment unit uses the detection unit to detect information related to relative displacement (for example, relative displacement of the initial displacement of the main portion or the displacement between the movable shielding member and the main portion during exposure) between the movable shielding member and the main portion. And according to this information, the adjustment unit controls the driving unit that drives the movable shielding member, during the scanning exposure on the substrate by the illumination light. Therefore, even in the case as described in the prior art where the responsiveness of the actuator of the vibration isolation unit in the main portion (the first column), the driving unit of the movable shielding member which driving portion mass is small and secures high responsiveness can correct the relative displacement (that is the relative error) described above. Thus, the movable shielding member can follow-up the mask sufficiently, and does not lose its shielding properties. In this case, the driving unit may use a conventional rotary motor; however, it is preferable for the driving unit to be a linear motor. This is because linear motors generate less vibration compared to rotary motors, and are capable of high-powered driving, as well as excel in controllability. As a consequence, the position controllability of the movable shielding member itself improves.
With the second scanning exposure apparatus according to the present invention, the exposure apparatus can further comprise: a measurement unit which measures a relative displacement between the first column and the second column; and an adjustment unit which adjusts a positional relationship between the movable shielding member and the main portion in accordance with the relative displacement measured by the measurement unit. In such a case, when the mask and the substrate are synchronously moved, the measurement unit measures the relative displacement between the first column and the second column. And in accordance with the relative displacement measured, the adjustment unit adjusts the positional relationship between the movable shielding member and the main portion. Therefore, the movable shielding member can follow-up the mask sufficiently, and does not lose its shielding properties.
In this case, when the exposure apparatus further comprises a driving unit which drives the movable shielding member during scanning exposure of the substrate with the illumination light, the adjustment unit can control the driving unit based on a detection result of the measurement unit. In such a case, the measurement unit can measure the initial displacement of the first column or the relative displacement between the first column and the second column during exposure, and in accordance with the measurement results, the adjustment unit drives the driving unit. Therefore, even in the case where the responsiveness of the actuator is low as in the prior art, the relative displacement described above (that is, the relative error) can be corrected with the driving unit of the movable shielding member having a low mass and capable of securing high responsiveness. Thus, the movable shielding member can follow-up the mask sufficiently, and does not lose its shielding properties.
With the second scanning exposure apparatus according to the present invention, in the case the exposure apparatus comprises the measurement unit, if the measurement unit is capable of measuring an absolute amount of relative displacement between the first column and the second column, the exposure apparatus can further comprise: a decision making unit which decides whether the relative displacement between the first column and the second column in a static state is within a permissible value based on a measurement value of the measurement unit; and a correction unit which corrects a positional error caused by the relative displacement by providing a zero offset corresponding to the relative displacement to the adjustment unit or a position control system of the first column, when a result of the decision making unit is affirmative.
For example, in the case distortion occurs over the elapse of time on the floor where the first column and the second column are respectively set and a static relative displacement occurs between the first column and the second column, when considering a coordinate system with the first column, the optical axes of the respective optical members on the first column side and the optical axes of the respective optical members on the second column side deviates by the distortion of the floor supporting the second column. When this occurs, the origin of the first column side and the origin that the driving unit of the movable shielding member recognizes does not coincide. In this case, if the adjustment unit continues to control the driving unit based on the measurement results of the measurement unit as described earlier without recognizing the shift, the error of the static relative displacement is consequently included in the measurement result itself. Therefore, a synchronous error (positional error) occurs between the movable shielding unit and the mask. To cope with such situation, with the present invention, the decision making unit decides whether the static relative displacement between the first column and the second column in a static state is within a permissible value. And when the decision is affirmative, the correction unit corrects the positional error caused by the relative displacement by providing a zero offset corresponding to the relative displacement to the adjustment unit or the position control system of the first column. Therefore, even when a static relative displacement occurs between the first column and the second column over the elapse of time, the shielding properties are not affected and are kept from losing its properties.
In this case, the xe2x80x9cpermissible valuexe2x80x9d described above is the threshold value determined within the range where the zero offset can cope with. Accordingly, when the correction cannot be coped with the zero offset, it is preferable for the exposure apparatus to further comprise a warning unit, which arises a warning, when the result of the decision making unit is negative. By doing so, the operation can acknowledge that a relative displacement exceeding the limit has occurred between the first column and the second column, and can take appropriate action by this warning. Thus, failure in exposure can be avoided in advance. The warning unit may be of a type showing the abnormal state on the display unit by literal information, or a type arising a warning by sound (speech), or by a warning lamp.
According to the third aspect of the present invention, there is provided a third scanning exposure apparatus which synchronously moves a mask and a substrate to transfer a pattern on the mask onto the substrate, the exposure apparatus comprising; a main portion which exposes the substrate with an illumination light via the mask; a movable blade which limits an illumination area on the mask; and an actuator which drives the movable blade in a synchronous movement direction of the mask and the substrate, the actuator being independent at least in respect to vibration from the main portion.
With this exposure apparatus, the actuator driving the movable blade which is the major cause of vibration during scanning exposure in the synchronous movement direction of the mask and the substrate, is arranged separately in respect to vibration from the main portion. Therefore, the vibration of the movable blade and the actuator is not the cause of vibration in the main portion. Also, the movable blade limits the illumination area on the mask, therefore usually only needs to prevent the irradiation of illumination light for exposure on the area outside the shield strip arranged in the periphery of the pattern area on the mask. The width of the shield strip is normally 1.5-3 mm, or even wider. The accuracy required, therefore, is substantially moderate, even when considering the vibration of the main portion caused by driving the mask the defocus of the movable shielding member, and the distortion of the optical system. Accordingly, when the pattern formed on the mask is transferred onto the substrate with the mask moved in synchronous with the substrate based on the scanning exposure method in a state where the mask is illuminated by the illumination light, the movable shielding member can substantially ensure that the area outside the shield strip in the periphery of the pattern area on the mask is kept from being irradiated by the illumination light. This eliminates a major cause of vibration on the main portion side during scanning exposure, and as a consequence, the exposure accuracy can be improved.
According to the fourth aspect of the present invention, there is provided a fourth scanning exposure apparatus which synchronously moves a mask and a substrate to transfer a pattern on the mask onto the substrate, the exposure apparatus comprising; an illumination system which illuminates the mask with an illumination light; a movable blade which sets an illumination area on the mask; and an actuator which drives the movable blade in a direction corresponding to a direction perpendicular to a first direction and has a static holding force, the first direction being a synchronous moving direction of the mask and the substrate and the direction perpendicular to the first direction being a second direction.
With this apparatus, the mask and the substrate is moved in synchronous in a state where the illumination system illuminates the mask with the illumination light, and the pattern formed on the mask is sequentially transferred onto the substrate by a scanning exposure method. During this scanning exposure, in order to prevent unnecessary portions (portions other than the pattern area on the mask) from being irradiated by the illumination light, the movable blade is arranged to set the illumination area on the mask. With the movable blade, in respect to the second direction perpendicular to the first direction in which the mask and substrate are moved in synchronous, the blade need only to be driven prior to scanning exposure to set the size of the illumination area. That is, the blade does not have to be driven during scanning exposure. In this case, an actuator having static holding force is used to drive the movable blade in the second direction, therefore, when the movable blade is stopped in respect to the second direction during scanning exposure, the servo of the actuator can be turned off. Thus, hunting (vibration) is not generated.
In this case, the exposure apparatus may further comprise an actuator which drives the movable blade in the first direction, the actuator being independent at least in respect to vibration from a main portion which exposes the substrate with an illumination light via the mask.
According to the fifth aspect of the present invention, there is provided a first method of making an exposure apparatus which is a scanning exposure apparatus synchronously moving a mask and a substrate to transfer a pattern on the mask onto the substrate, the method of making an exposure apparatus comprising; providing an illumination system which illuminates the mask with an illumination light; providing a driving system which drives the mask and the substrate in synchronous; providing a movable blade which limits an illumination area on the mask; providing a linear motor which drives the movable blade; and providing a separate portion where the linear motor is arranged, the separate portion being independent at least in respect to vibration from a main portion which exposes the substrate with an illumination light via the mask.
With this method, by mechanically, optically, and electrically combining the illumination system, the driving system including the mask stage and the substrate stage, the movable blades and the linear motors, the separate portion where the linear motors are arranged, and other various components the first scanning exposure apparatus in the present invention can be made. In this case, this method can further include the step of providing a projection optical system which projects the pattern image of the mask onto the substrate. In such a case, a projection exposure apparatus based on the method such as a slit scan or a step and scan method can be made.
According to the sixth aspect of the present invention, there is provided a second method of making an exposure apparatus which is a scanning exposure apparatus synchronously moving a mask and a substrate to transfer a pattern on the mask onto the substrate, the method of making an exposure apparatus comprising steps of: providing a main portion which exposes the substrate with an illumination light via the mask; providing a first column where the main portion is arranged; providing a movable shielding member which limits an illumination area of the illumination light on the substrate in accordance with synchronous movement of the mask and the substrate; and providing a second column which is independent from the first column in respect to vibration, the movable shielding member being arranged in the second column.
With this method, by mechanically, optically, and electrically assembling the main portion, the first column, the movable shielding member and the second column, and other various components the second scanning exposure apparatus in the present invention can be made. In this case, this method can further include the step of providing a projection optical system which projects the pattern image of the mask onto the substrate. In such a case, a projection exposure apparatus based on the method such as a slit scan or a step and scan method can be made.
With the method of making the second exposure apparatus, the method of making an exposure apparatus can further comprise a step of providing a fixed field stop which sets the illumination area of the illumination light on the substrate to be incorporated into the main portion. In such a case, an excellent exposure apparatus that avoids exposure on unnecessary areas on the substrate (generate the positional error of the illumination area and the mask), and stabilizes the image plane (surface of substrate) illuminance can be made.
With the method of making the second exposure apparatus, the method of making an exposure apparatus can further comprise the steps of: providing an illumination optical system which irradiates the illumination light onto the mask; and providing the movable shielding member to be arranged within the illumination optical system and a portion of the illumination optical system to be located further on a side of the mask than the shielding member, the portion of the illumination optical system to be arranged in the main portion. In such a case, a scanning exposure apparatus with the total mass of the main portion side reduced, the stability improved and the vibration reduced by lowering the center of gravity can be made.
Furthermore, by performing exposure using the scanning exposure apparatus in the present invention in a lithographic process, a multiple layer of patterns can be formed with high overlay accuracy on a substrate, therefore, microdevices with high integration can be produced with high yield, thus improving the productivity. Therefore, from another aspect of the present invention, there is provided a device manufacturing method that uses the exposure apparatus of the present invention.